25 replies to this topic

[I'm a Red Motor fiend]

On my current build I have gone back to running a Holley blue pump.
I have noticed that since doing this my charging rate is below 13V whereas when I ran a mechanical pump it charged at 13.7V no problem.
Alternator is an 85a from a VN I had laying around (Very old)

My question is, do I get a new 85a alternator or should I go up to something like a 120a?
I run a thermo fan also.

[LC-GTR-1969]

On my current build I have gone back to running a Holley blue pump.
I have noticed that since doing this my charging rate is below 13V whereas when I ran a mechanical pump it charged at 13.7V no problem.
Alternator is an 85a from a VN I had laying around (Very old)

My question is, do I get a new 85a alternator or should I go up to something like a 120a?
I run a thermo fan also.

 

85 amps is heaps in my opinion. Im running a measly 60 amp with holley blue pump, electric water pump and twin thermos. Not ideal but when my 85amp unit died I already had a good 60 amp so just used it. I'd be looking for possible voltage drop- where are you measuring the output from?

 

BTW- Electrics is far from my strong point but you may find a poor earth, a dodgy terminal or too small gauge wire could be dropping your charge rate? 

[I'm a Red Motor fiend]

Honestly I think it's just the clapped out old 85a unit that can't keep up with the pump.
There aren't any issues anywhere else and the charge drop rate was instantaneous from mechanical to electric pump change.
I was thinking 85a would be plenty so I think I'll just purchase a new 85a unit unless anyone else thinks I need more?

[RallyRed]

Hi mate, my white LJ track car runs a Blue Holley, stock alternator. No dramas, been like it for 6 years.

[Rockoz]

For an alternator to work charging the battery, its voltage output needs to be more than the voltage of the battery.

So provided you are above 12 volts, you shouldnt have an issue.

If you are running a normal charging circuit with the indicator light, provided the light is off, then the alternator is doing its job.

Check it in darkness if you are concerned. If it has a very light flicker, then you may be heading for problems.

If it isnt glowing, then all is good.

 

Cheers

 

Rob

[I'm a Red Motor fiend]

Thanks Rob.
Went down to repco before and bought a new 85a unit. Changed it out, went for a squirt and guess what? Only about 12.2 volts.
Guess the old one was working. Oh well.
Second day back on the road today after winter hibernation and I'm loving it.
Now, back to polishing SU needles to get the tune right.....

[Rockoz]

If you feel the need to play with car electrics, there is a relatively cheap meter you can buy that will make life easier.

 

It is sold by Jaycar electronics. It is a multimeter and a clamp amp meter that will measure ac and dc current.

I bought one years ago and it did me good service. It was under a hundred bucks, compared to the "name" meters at around a grand.

And it did the job very well indeed.

 

You can clip it over a wire and measure the current flowing through the wire.

Its great for checking alternators.

But my favourite check for an alternator is listening.

You can hear them whistle a bit when they are charging.

Once you know what to listen for its as good a check as any other to determine if it is working.

 

 

Cheers

 

Rob

[LC-GTR-1969]

Thanks Rob.
Went down to repco before and bought a new 85a unit. Changed it out, went for a squirt and guess what? Only about 12.2 volts.
Guess the old one was working. Oh well.
Second day back on the road today after winter hibernation and I'm loving it.
Now, back to polishing SU needles to get the tune right.....

 

if your meter is reading correctly, that charge rate is showing you have something amiss. Where is your battery located? I get 13.2v running battery in boot, 60 amp alternator with holley blue, twin thermos and electric water pump. I had a similar issue and it was a dodgy crimp that caused voltage drop. Took quite a while to find.

[I'm a Red Motor fiend]

Battery is in boot.
Maybe I will re visit my pump wiring.
As I said earlier, charge rate was spot on before I installed the Holley blue.

[I'm a Red Motor fiend]

This is doing my farkin life in. Still can't get the alternator to stay excited .
New battery
New Bosch 85a alternator
New 2w charge light
The belt is not slipping
First startup I get 13.2 volts all good at the battery, alternator and volt gauge.
Warm up for a bit and hit the road. Get above 2000rpm voltage drops to 12.2.
Pull over and at idle comes back up to 13.2.
But this is short lived as once fully warmed up it stays at 12.2 no matter what engine speed and the longer I drive it drops below 12v.

I can turn the fans and fuel pump off while driving and I see a tiny bit more voltage but nothing over 12.2v.

Why the hell does it excite on initial cold startup but then craps out????

[gtrboyy]

Is there a voltage drop or something weird happens when it gets heat in bay etc?

 

Checked gauge compared to multimeter?

 

 

I've always looped white load sensing wire to alternator stud.Used 70a(?) vk efi alternator & vn/s 85a on torrie to run twin thermo,efi pump,hei,ecu etc no issues.

 

 

Can't see it needing diode for charge light unless msd/cdi.

[I'm a Red Motor fiend]

Yeah sense wire looped to alternator post.
Have MSD and have inline diode too....

[rodomo]

Something is heating up and causing the voltage drop. Check all connections. AMP meter?

 

Heat causes resistance causes heat causes resistance causes heat causes resistance causes heat causes resistance causes heat

Edited by rodomo, 20 December 2020 - 10:39 PM.

[Rockoz]

What is the voltage with just the ignition on?

Im gathering the pump will start running with the ignition.

Disconnect the pump and check voltage again.

Remember that the test tool you are using may not be accurate, especially if it is a cheap one.

So check voltages against each other rather than the value indicated.

With the car running it should be as close to 13.8 as possible.

If the alternator senses that the battery requires no more power, it will drop its voltage output.

Thats stops overcharging.

A DC clamp meter is invaluable in situtations such as this.

 

Cheers

 

Rob

[I'm a Red Motor fiend]

Ignition on 12.2V
I wired the pump via a switch directly from the battery in the boot so is independent from the ignition.
Turning the pump off with the engine running sees very little voltage increase.

[I'm a Red Motor fiend]

Rodomo has got me thinking also. The only other change with this build was using HM9C headers which puts the solenoid and wiring to it very close to number 6 primary pipe.
I will try re route the wiring best I can to see if this helps.

[claysummers]

Why i don't like extractors....

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[Rockoz]

Im just wondering if your meter is wrong.

What type is it?

Are you using a multimeter, or an in car gauge?

Kind of why I was saying to check the voltages against each other rather than worrying about the actual number.

If your meter is reading wrong, the figures you are getting could be okay.

 

Cheers

 

Rob

[I'm a Red Motor fiend]

As above, I measured 13.2v on startup at Alternator and battery and the gauge showed the same value.

[Rockoz]

13.2 is a little low I would think.

I would be expecting closer to 13.8 as the battery has just had a huge drain starting it.

 

What you are describing though sounds a lot like a loose connection or earth.

With the battery in the boot, are you running a decent earth wire to the front, or relying on the chassis?

 

Cheers

 

Rob

[I'm a Red Motor fiend]

Yeah I think you have got it Rob.
Relying on chassis. I will run a cable from the back up to the front.
Fresh build means fresh painted parts. I think the alternator is not earthed properly due to the brackets being all painted.
I scraped a little off of the top belt tension bracket and went for a run. I saw 14v on and off down to 12.5 and the needle kept flickering like it wanted to push back up to 14v.
So the system is capable but something is stopping it which really speaking would have to be a bad earth I reckon.

[gtrboyy]

How many earths & where?

 

engine block to chassis rail

battery negatiive to bumper bar bolt in boot

Think I also had bellhousing bolt to chassis rail...spare cable that was fitted there so used it lol.

 

Other than that usual bare metal surface & clean before bolting things down & checked with multimeter.

 

During crazy 202 days had wrap extractors & heatproof as it liked to melt all wiring underneath...also broke alternator brackets.

[claysummers]

I have run earth through chassis with no issue for 50000 miles in an EK sedan. Used big fat orange coated cable to starter. Starter bottom bolt to subframe bolt. Negative to tail light housing stud. Alternator earth to radiator bolt. Big mother GMH battery and reduction gear starter.


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[I'm a Red Motor fiend]

Earthed from battery -VE to chassis rail just behind rear wheel using 80 sq m cable.
Upgraded earth wire from head to chassis rail adjacent alternator.

Maybe I'll try an earth cable from alternator to chassis also.

[Rockoz]

Using the chassis as the earth was a cost cutting venture as much as anything.

Worked okay with the battery close to the main current draw.

When they were built originally, paint was thin and in places non existent.

You will never see a metal boat using the hull as an earth.

Even polishing stuff can increase its electrical resistance by creating a film on the item.

 

You could test the theory with a small wire.

Some 3 or 4mm will do.

But put a fuse in it of around 10A.

Run it from the battery to the alternator.

If it starts taking the current and your voltages increase, then you know where the problem is.

Steel is nowhere near as conductive as copper.

Think about all the joins it has to go through as well, jumping from panel to panel.

 

Minimise the number of earth points as much as you can as well.

You may start getting voltage differences between them and that will cause rust very quickly.

 

Cheers

 

Rob